Broad comments such as yours below should come with the necessary
warnings that they lack accuracy because they simply do not properly
consider the full field.
Studies of the dyes used in -R CDs, as well as the metal coating and
lacquer coating technologies, have shown massively variable results. In
some tests, especially during the periods when manufacturers were having
difficulties maintaining enough product, just prior to recordable DVD
technology becoming commonplace, some CD-R media began failures in as
little as 6 months from use. Many of these were made in countries with
poor quality controls in their factories, and many of those products are
no longer being produced, but many can have them in their collections.
Although I have not researched this issue recently, when I last checked,
very few CD-R media had expected 150 year ranges. As of a few years
back only specific dyes and use of sputtered gold came even close to 100
plus years expectations.
At the time I did research, archivists and professional services,
including the Library of Congress, were suggesting 10-20 year cycling
for critical materials and 35-40 years for highly redundant data.
Simply put, -R recordable technologies rely on organic dyes which are
vulnerable to light damage, and with CDs, physical damage, since they
are poorly protected only on one side by polycarbonate. Detachment of
the metal layer, oxidation of the aluminum surface due to mishandling or
the lacquer coating having been poorly applied with either air bubbles
or moisture had been fairly common.
The technologies used in -RW materials is quite different, and face
other antagonists, but may ultimately be more stable than -R. DVD
writable technologies differ in that the data surfaces are sandwiched
between two layers of polycarbonate plastic. They may prove more or less
stable as a result, but are better protected against physical damage.
However, just to reiterate, 150 years is an overstatement, and yes, some
CD -R materials have degraded in months and years. They may be the
exception, but implying that CD materials are regularly safe from data
lose for over a century is probably as equal an exaggeration as to state
that all CD -R materials will fail in 5 years.
For those who are concerned about their data on CD media, I would
suggest reviewing your CD-Rs every year or two for possible loss of
data, use sputtered gold coated CD-Rs for best longevity, and recognize
that a bigger problem may be the burners and drive technologies design
changes making media difficult to read, which may also suggest that
reburning every few years may somewhat protect you from those changes if
you upgrade your burners. Loss of media reading devices is probably
even a bigger risk than the media failure, but both need to be considered.
Art
